Sunday, December 8, 2013
By SAMANTHA LANGLEY-TURNBAUGH and LISA BELANGER
Lead contamination of soils is a widespread problem, especially in urban areas such as Portland. Urban environments often have lead levels of more than 1,000 milligrams per kilogram and reported values as high as 50,000 mg/kg, while natural soil levels are generally below 50 mg/kg.
USM research focused on the Portland peninsula and Peaks Island found that the soils there have a high lead burden. Lead levels routinely (more than 90 percent of properties sampled) exceed acceptable levels, with an average concentration of 1,500 mg/kg.
The Environmental Protection Agency Final Rule established a soil lead hazard at 400 mg/kg for bare soil in play areas, while Maine's Remedial Action Guideline (the standard for what level of contamination merits further investigation or remediation) is 170 mg/kg.
Lead is highly immobile in soils; thus, lead deposited in soil is a persistent and long-term source of lead exposure, particularly for children. Lead deposited in soils will remain there for thousands of years.
Lead is the single most important environmental health problem affecting American children. One out of every 20 U.S. children suffers from lead poisoning.
There is no known safe level of lead in blood. Lead is a highly toxic neurotoxin, especially to children, causing irreversible cognitive and behavioral impairments, lower IQs, difficulties in reading, speech delays, attention deficits and increased violent behavior.
In addition, lead ingestion by a woman of childbearing age may affect both the woman's health and that of her fetus, for lead is stored in the bone and released during gestation.
Commonly recognized sources of lead exposure include lead-contaminated paint, dust and water. However, recent concerns include contributions to blood lead levels from soils, and several studies have found that soil lead is an important contributor to children's blood lead levels and lead poisoning.
In fact, environmental health researchers acknowledge that urban soil is a significant sink of bioavailable lead that has not been regulated or included in a comprehensive prevention strategy. Thus, it is a public health issue. In some cases, lead-contaminated soils have contaminated vegetable crops in backyard gardens, and exposure may be the result of plant uptake of lead from soils, or from leaded dust accumulated on plant surfaces.
Certain species of plants, known as "hyperaccumulators," can accumulate high levels of metals in their tissues without showing signs of toxicity. Such plants can be used to clean up heavy metal-polluted soils if their biomass and metal content are large enough to complete remediation within a reasonable period of time -- a process that is called "phytoremediation."
We successfully used the innovative, low-tech method of phytoremediation to reduce lead levels in surface soils. Prior to this project, no program existed in Portland or in Maine to help residents of high-risk neighborhoods reduce exposure to lead in residential soils.
Lead poisoning is preventable, and there are ways residents can protect themselves from exposure to lead in contaminated soils and plants.
First, have your soil tested, especially in bare soil areas, including gardens, children's play areas and dog runs, and the drip zones along house foundations. Your cooperative extension office can assist you with soil testing information, sampling kits and costs.
If your soils test high in lead, there are precautions you can take to reduce your exposure. You may choose to have the contaminated soils removed and replaced with clean soil.
If this is not practical or affordable, then you should take steps to eliminate your exposure to the contaminated soil and dust. These steps should include covering any bare soil areas with plants or mulch to reduce contact and dust; covering drip zones and walkways with crushed rock, and planting gardens in raised beds or containers.
In addition, you should wash all produce grown in your yard thoroughly, peel root crops before eating and discard the outer leaves of vegetables.
It is also important to have your children's blood tested regularly; make sure they regularly wash their hands after playing outside; remove shoes before entering the house, and ensure they eat a diet high in calcium, iron and vitamin-rich foods, because these nutrients reduce lead absorption and protect the body from the harmful effects of lead.
Samantha Langley-Turnbaugh is a professor of environmental science at the University of Southern Maine, and Lisa Belanger is USM's director of health services.
– Special to the Press Herald